1. Field of Invention
This invention relates generally to the production of polyhydroxyalknoic acids, specifically to the microbial production of polyhydroxyalkanoates (PHA) from substrates which are bacteriocidal and which cannot be used as a source of carbon for growth or PHA production.
2. Description of the Related Art
Polyhydroxyalkanoates (PHAs) are polymers generated by microorganisms as energy storage vehicles. PHAs are biodegradable and biocompatible polymers that can be used as alternatives to petrochemical-based plastics such as polypropylene, polyethylene, and polystyrene. In comparison to petrochemical-based plastics, which are not biodegradable, PHA plastics afford significant environmental benefits.
Despite the advantages of using PHA plastics, the high price of PHAs compared to the low price of petrochemical-based plastics have significantly limited their widespread use. PHAs are commercially produced in bacterial fermentation processes wherein a carbon substrate is used to drive microorganism growth and PHA synthesis. Since carbon is used in significant quantities in the PHA synthesis process, carbon inputs largely determine the overall price of PHA. Accordingly, in order to make PHA competitive with petrochemical-based polymers, there is a significant need to develop novel sources of carbon for PHA synthesis.
Prior to the applicants' discovery, it was believed that carbon substrates used to produce PHA were limited to substrates that could be used by microorganisms as a source of carbon for growth, such as sugar or high fructose corn syrup. Since carbon forms the backbone of the PHA molecule and the cellular structures required to enable intracellular PHA synthesis, in the past, substrates that could not be used by microorganisms as a source of carbon for cellular growth or PHA synthesis, or carbon-based substrates that were either growth-limiting or growth-inhibiting, that is, bacteriostatic or bacteriocidal, respectively, were not considered useful for the PHA production process.
In U.S. Pat. No. 6,395,520, Babel, et al., herein incorporated by reference in its entirety, disclose a PHA production method for the use of substrates that exhibit the phenomenon of substrate inhibition, but only in cases of excess substrate, wherein the capacity of microorganisms to use the carbon within substrates for PHA production is determined by substrate concentration. The microorganisms described by Babel, et al. are metabolically capable of using particular substrates as a source of carbon for growth and PHA synthesis as long as the concentrations of those substrates are sufficiently low. Babel, et al. do not disclose a method for the use of substrates that cannot be used at all by PHA-producing microorganisms as a source of carbon for growth or PHA synthesis at any concentration, including at very low concentrations.
Volatile organic compounds (VOCs) are compounds that form gaseous vapors under normal atmospheric pressures and temperatures and engage in photochemical reactions to form oxidized photochemicals. VOCs contribute heavily to the formation of tropospheric pollutants such as ozone and smog, and human exposure to airborne volatile organic compounds is known to cause a variety of adverse health effects, including liver damage, brain damage, and cancer. VOCs are considered to represent one of the most important classes of soil, air, and groundwater pollutants in the United States. VOCs, are emitted by a wide range of industrial processes, including paint manufacturing, chemical synthesis, and wastewater chlorination. VOCs, which, as used herein, excludes methane in some embodiments, cannot be oxidized into non-toxic compounds or used as growth substrates by most naturally-occurring microorganisms, and subsequently persist in the environment as highly recalcitrant pollutants.